Willows are a family of trees and shrubs which have many differences in size and type of growth, but are very much alike in other respects. There are about 350 species of this plant in all the world, usually found on moist soils in cooler zones in the Northern Hemisphere. Many hybrids are known, both naturally occurring and in cultivation, because willows are very fertile between their own species.

Some smaller species may also be known by the common names osier and sallow; the last name comes from the same word as the Latinsalix.